Somewhere in deep space, in the heart of the Galaxy Police Headquarters, lies an evil being, who's power and abilities are almost unimaginable. That being is known as Kain. It took Kain over a hundred years to do it, but now he's finally found a way to break out of his prison in subspace. As he escapes, he destroys GP headquarters. His next destination: the Earth in the past. As Kain disappears into the past, Tenchi begins to experience strange phenomena such as his hand disappearing for a moment. Soon, Tenchi feels himself getting sucked away. It turns out now that the old universe has changed, and Tenchi never existed. Currently the disturbance in the universe only revolves around the Misaki family, but soon, the rest of the universe will change also. Washu manages to shield Tenchi and company from the new universe, but the shield can't hold forever, and then Tenchi will be no more. The answer is in the past, and Washu can get them there, but then what?

Washu doesn't know much, but she does know that something happened to Tenchi's mother Achika in the past. Thus Tenchi and his friends journey into the past, where his mother and father are still in highschool. No one knows what or when anything will happen, so the only solution seems to be to keep an eye on Achika and make sure nothing happens to her. Everyone goes undercover: Aeka, and Ryoko pose as school girls, Mihoshi as a school teacher, and Kiyone... as various things. Unfortunately Ryoko and Aeka are up to their usual fighting which as usual creates a mess. But this time it could create an even bigger problem since they're antics could interfere with Achika and Nobiyuki getting together in the first place, which would mean Tenchi still wouldn't be born.
    Eventually Washu manages to put together enough information that they pinpoint the time and location of Kain's attack. That leaves only one question: ‘How do they stop Kain', who is a being so powerful that the emperor of Jurai died just trying to contain him. With no Jurai power, or Galaxy Police to assist, surely Tenchi can't stop Kain alone. And who is that mysterious looking guy that's always watching Achika anyhow? Well Washu's always got a plan, so perhaps there is a way.